1. Technical Field
The present invention relates to a television tuner for tuning in a television radio wave by changing a tuning frequency on the basis of a reference frequency for each channel number, the tuning frequency that is tuned being set as the frequency of a channel number, when setting the channel number, and a television receiver having the television tuner.
2. Prior Art
FIG. 6 is a block diagram showing an exemplary configuration of the essence of the conventional television receiver. In this television receiver, an RF (Radio Frequency) signal received by an antenna 11 is tuned and amplified by an RF amplifier 12 that is a tuning circuit of an electronic tuner. The tuned and amplified RF signal is mixed with an oscillating signal from a local oscillator 14 phase locked by a PLL (Phase Lock Loop) circuit, not shown, by a mixer 13, and then converted into an IF (Intermediate Frequency) signal. A tuner 15 is composed of the RF amplifier 12, the local oscillator 14 and the mixer 13.
The IF signal is amplified by an IF amplifier 16, and band limited by a SAW (Surface Acoustic Wave) filter 17, whereby the band-limited IF signal has its level detected by a detector 18. The detected result of the level is passed to an AGC (Automatic Gain Control) circuit 19, which then outputs a gain control signal on the basis of the detected result given. The RF amplifier 12 has its gain controlled in accordance with the gain control signal output from the AGC circuit. With this gain control, when a strong electric field signal is received, the tuner 15 itself is prevented from being overloaded and causing false modulation.
The IF signal has the color signals R, G, B, a horizontal synchronizing signal and a vertical synchronizing signal extracted in a video signal processing portion 20, the extracted color signals R, G, B being input into a CRT 21. In the CRT 21, the color signals R, G, B are turned into the electron beams having respective intensities, and the horizontal scanning and the vertical scanning are performed by a drive circuit, not shown, based on the horizontal synchronizing signal and the vertical synchronizing signal.
The IF amplifier 16, the SAW filter 17, the detector 18, the AGC circuit 19 and the video signal processing portion 20 are integrally formed on an IC 26.
The RF amplifier 12, the local oscillator 14 and the video signal processing portion 20 are operated under the control of a microcomputer 22 connected via a bus 27. The microcomputer 22 has a ROM (Read Only Memory) 23 storing its operation program and the reference frequency of the television radio wave for each channel number, a RAM (Random Access Memory) 24 temporarily storing the data associated with the operation, and an E2 PROM (Electrically Erasable ROM) 30 storing the channel set frequency for each channel number.
The microcomputer 22 is connected to an operation console 25 with the operation buttons, and is supplied with the detected result of the IF signal level detected by the detector 18.
The frequency of television radio wave is allocated to each country or area by the CCIR (International Radio Committee) to avoid the interference, in which the frequency for each channel number is greatly different depending on the country or area.
In the apparatus manufacturing company for producing television receivers and video tape recorders, a channel plan that is a list of reference frequencies for the channel numbers is created for each destination with reference to a list of channel receiving frequencies for the destination as defined by the CCIR, and stored in the ROM for the microcomputer incorporated in the apparatus to be produced.
The user can make a channel setting operation simply in an automatic or manual channel preset mode, using this channel plan.
The maximum amount of drift from the center frequency (reference frequency) of each channel number is set up to make it possible to receive the broadcasting even in the case where the broadcasting frequency is off the reference frequency, or a newly opened broadcasting station broadcasts at a frequency off the reference frequency in the channel plan, whereby the broadcasting can be received within a set range. This range is referred to as a xe2x80x9ccover rangexe2x80x9d, which is assigned to the plus or minus side from the center frequency of each channel number.
As above constituted, in the case where the channel is set up in an automatic channel preset mode, the television receiver is tuned to a television radio wave for each channel number by changing the tuning frequency of the RF amplifier 12 within the cover range around the center frequency that is the reference frequency of each channel number stored in the ROM 23, and the tuning frequency that is tuned is set up as the frequency of the channel number successively and stored in the E2 PROM 30.
When the channel number is selected, the television radio wave at the frequency of each selected channel number that is set up and stored in the E2 PROM 30 is received.
Also, in the case where the channel is set up in a manual channel preset mode, the television receiver is tuned to a television radio wave of the selected channel number by changing the tuning frequency of the RF amplifier 12 within the cover range around the center frequency that is the reference frequency of a selected channel number stored in the ROM 23, and the tuning frequency that is tuned is setup as the frequency of the channel number successively and stored in the E2 PROM 30.
When the channel number is selected, the television radio wave at the frequency of each selected channel number that is set up and stored in the E2 PROM 30 is received.
[Problems to be Solved]
In the conventional television receiver, in the case where the television radio wave of the channel number for a broadcasting station had extremely low power due to the reason that the broadcasting station was located at the remote site, a wide band RF amplifier (booster) was attached externally to amplify the television radio wave from the antenna and pass the amplified radio wave to the tuner. However, if the television radio wave for all the channel numbers is amplified by the booster, the television radio wave of the channel number at which the power of radio wave is not extremely low is too strong, giving rise to some input distortion. Therefore, there is a problem that the recipient must turn on or off the booster depending on whether the screen condition is excellent or not.
As a technique to solve this problem, a xe2x80x9ctelevision receiverxe2x80x9d containing a radio frequency booster for wide band amplification without having to purchase the booster and attach it externally was disclosed in the Unexamined Japanese Patent Application Publication No. Sho61-206325.
This invention is achieved in the light of the above-mentioned problems, and it is an object of the invention to provide a television tuner containing a wide band RF amplifier and not requiring to turn on or off the wide band RF amplifier for each channel, in which the excellent characteristics of image quality can be attained, irrespective of whether the television radio wave is weak or strong in the electric field.
Also, it is another object of the invention to provide a television receiver with the television tuner.
[Means for Solving the Problems]
According to a first aspect of the invention, there is provided a television tuner having a reference frequency for each channel number of television radio wave, which can be tuned to a television radio wave of a channel number by changing a tuning frequency of an RF amplifier on the basis of the reference frequency of the channel number, when setting the channel number, the tuning frequency that is tuned is set up as the frequency of the channel number, and the television radio wave of the set frequency is received as the television radio wave of the channel number, the television tuner characterized by comprising a booster for boosting the television radio wave to be fed to the RF amplifier, inhibit means for inhibiting the operation of the booster by an operation from the outside, and memory means for memorizing an operation state of the inhibit means corresponding to the channel number when setting the tuning frequency as the frequency of the channel number, wherein when the channel number is selected, the inhibit means is placed in the operation state memorized by the memory means corresponding to the channel number.
This television tuner has a reference frequency for each channel number of television radio wave, and can be tuned to accept a television radio wave of a channel number by changing the tuning frequency of the RF amplifier on the basis of the reference frequency of the channel number, the tuning frequency that is tuned being set up as the frequency of the channel number, and the television radio wave at the set frequency being received as the television radio wave of the channel number. The booster is provided to boost the television radio wave to be fed to the RF amplifier, and the inhibit means inhibits the operation of the booster upon an operation from the outside. When the tuning frequency is set as the frequency of the channel number, the memory means memorizes an operation state of the inhibit means corresponding to the channel number. And when the channel number is selected, the inhibit means is placed in the operation state memorized by the memory means corresponding to the channel number.
Thereby, it is possible to realize the television tuner containing a wide band RF amplifier, and not requiring to turn on or off the wide band RF amplifier for each channel, in which the excellent characteristics of image quality can be obtained irrespective of whether or not the television radio wave is weak or strong in the electric field.
According to a second aspect of the invention, there is provided a television tuner having a reference frequency for each channel number of television radio wave, which can be tuned to a television radio wave of a channel number by changing a tuning frequency of an RF amplifier successively on the basis of the reference frequency of the channel number, when setting the channel number, the tuning frequency that is tuned is set up successively as the frequency of the channel number, and the television radio wave of the set frequency that is set up successively is received as the television radio wave of the channel number, the television tuner characterized by comprising a booster for boosting the television radio wave to be fed to the RF amplifier, inhibit means for inhibiting the operation of the booster, determination means for determining whether or not the signal level of the tuning frequency that is tuned to the television radio wave of the channel number is greater than or equal to a predetermined value, means for turning off the operation of the inhibit means, if the determination means determines that the signal level is not greater than or equal to the predetermined value, means for tuning in the television radio wave by changing the tuning frequency of the RF amplifier in a state where the inhibit means is turned off, and memory means for memorizing an operation state of the inhibit means corresponding to the channel number when setting the tuning frequency to which the means is tuned as the frequency of the channel number, wherein when the channel number is selected, the inhibit means is placed in the operation state memorized by the memory means corresponding to the channel number.
This television tuner has a reference frequency for each channel number of television radio wave, and can be tuned to a television radio wave of a channel number by changing a tuning frequency of the RF amplifier successively on the basis of the reference frequency of each channel number, when setting the channel number, in which the tuning frequency that is tuned is set up successively as the frequency of the channel number, and the television radio wave of the set frequency that is set up successively is received as the television radio wave of the channel number. The booster boosts the television radio wave to be fed to the RF amplifier, and the inhibit means inhibits the operation of the booster. The determination means determines whether or not the signal level of the tuning frequency that is tuned to the television radio wave of the channel number is greater than or equal to a predetermined value, and the turning off means turns off the operation of the inhibit means, if the determination means determines that the signal level is not greater than or equal to the predetermined value. The tuning means is tuned to the television radio wave by changing the tuning frequency of the RF amplifier in a state where the inhibit means is turned off, and the memory means memorizes an operation state of the inhibit means corresponding to the channel number when setting the tuning frequency that is tuned as the frequency of the channel number. When the channel number is selected, the inhibit means is placed in the operation state memorized by the memory means corresponding to the channel number.
Thereby, it is possible to realize the television tuner containing a wide band RF amplifier, and not requiring to turn on or off the wide band RF amplifier for each channel, in which the excellent characteristics of image quality can be obtained irrespective of whether or not the television radio wave is weak or strong in the electric field.
According to a third aspect of the invention, there is provided a television receiver comprising the television tuner as above described.
Since this television receiver comprises the television tuner containing the wide band RF amplifier, and not requiring to turn on or off the wide band RF amplifier for each channel as above described, the television receiver can be realized in which the excellent characteristics of image quality can be obtained irrespective of whether or not the television radio wave is weak or strong in the electric field.